Lubrication is the process or technique that reduces wear of one or both surfaces that move relative to each other in close proximity. Lubricants prevent or lessen wear and irritation between the surfaces.
Personal lubricants for intercourse are well known and are useful for providing lubricity to various parts of the body, such as mucous membranes (e.g. oral, rectal, vaginal). These compositions may be in the form of jellies, liquids, vaginal suppositories, oils or emulsions. When applied onto condoms, these lubricants also facilitate unrolling of the condom as well as preventing the surfaces of the rolled condom from sticking together as the products age in storage.
Water-based personal lubricants are water-soluble and are the most widely used personal lubricants. These lubricants are easy to clean up, non-staining to fabrics and are formulated to be nonirritating. The viscosity of these products can be altered by adjusting their water content and concentration of cellulose or other gel-forming hydrophilic ingredients. However, because water-based personal lubricants absorb into the skin and mucous membranes and evaporate, these lubricants have a tendency to dry out during use. Very often, the water-based lubricant has to be reapplied to extend the intimate activity. This is one of the chief drawbacks of water-based lubricants, since reapplication is distracting and “breaks the mood”.
To improve product lubricity, water-based lubricants are often formulated with high levels of polyhydric alcohols such as propylene glycol, glycerin or sorbitol that function as humectants. For example, the marketed K-Y® NATURAL FEELING® Liquid, which is described in U.S. Pat. No. 5,885,591 to Ahmad, et al. comprises about 30% glycerin, about 5% propylene glycol and about 10% sorbitol. In addition to polyhydric alcohols, surfactants are also added to water-based lubricants to reduce the attraction between water molecules, thereby making the lubricants more slippery and less sticky. For example, commercially available water-based lubricants of the ASTROGLIDE® series all contain surfactants such as polyquaternium-15.
Recent studies have shown that personal lubricants that contain polyhydric alcohols or surfactants may damage the vagina and rectum cell linings, potentially making the user more vulnerable to sexually transmitted diseases (STDs) (see O. Begay et al., AIDS Research and Human retroviruses, 27, 1-6, 2011; L. K. Wolf C&EN 90(50), 46-49, 2012). According to O. Begay, et al., the damaging effect is dependent upon osmolality of the lubricant. Osmolality is a parameter that indicates the overall concentration of the molecular ingredients in a composition. Osmolality is measured in moles (osmoles) of solute per kilogram of solvent. Mice that were exposed to lubricants with high osmolality were more susceptible to infections. Many water-based lubricants on the market have high osmolality, as they contain large amounts of ingredients such as propylene glycol, glycerin and sorbitol, which contribute to high numbers of moles of solutes per kg of solute.
A preferred type of personal lubricant is silicone-based. Silicone-based personal lubricants are very lubricious and do not dry out. Further, they are hypoallergenic, safe to use with condoms and are less damaging to cells because of their low osmolality. However, the main drawback of silicone-based lubricants is that they are greasy and can be difficult to cleanup.
To deliver the benefits of both water- and silicone-based lubricants, oil-in-water (o/w) emulsions-based lubricants have been developed and marketed. These lubricants are typically opaque or “milky” in appearance, which is caused by the difference in refractive index between the aqueous phase and the oil phase. LIQUID SILK® and SYSTEM JO® Hybrid are examples of emulsion-based personal lubricants.
To make the emulsion lubricants clear and transparent, and thus more appealing to consumers, two approaches have been taken. The first approach involves matching the refractive index between the two immiscible phases. The second approach involves the use of high concentrations of emulsifiers to form micro-emulsions. The oil droplets in the micro-emulsions are smaller than the light wavelength, thus making the emulsion appear clear. U.S. Pat. No. 6,139,848 to Ahmad, et al. discloses micro-emulsion-based lubricants, which are highly lubricious, clear and transparent. However, these micro-emulsion-based lubricants also have high levels of polyhydric alcohols (up to 45% w/w), which may harm vaginal cells.
An alternative to known water-based and silicone-based personal lubricants has been developed using hyaluronic acid (“HA”) as a lubricating component to relieve vaginal dryness. For example, U.S. Patent Application No. 2010/0284937 to Zhao, et al. teaches a vaginal lubricant comprising a high molecular weight HA and a low molecular weight component selected from low molecular weight HA and chitosan, wherein the low molecular weight component stabilizes the lubricant.
U.S. Patent Application No. 2009/0143331 to Strompoulis, et al., teaches a cosmetic composition comprising at least one polysaccharide such as HA and encapsulating at least one inhibitor of degradation into the polysaccharide.
U.S. Pat. No. 4,869,270 to Uneo, et al., teaches a condom comprising a coating made from polysaccharide such as HA, wherein the coating is an aqueous solution that contains 10-70% concentration of the HA.
U.S. Patent Application No. 2011/0171286 to Cecile, et al., teaches an HA gel formulation for treating skin, comprising hyaluronic acid and at least one additional constituent selected from the group consisting of vitamin B, C and E, wherein the formulation exhibits greater stability.
However, the exemplary prior art either teaches a composition that requires a special ingredient to stabilize the HA, a high amount of HA of at least 10%, or the viscosity of the taught composition is undesirably low, causing the lubricant to be too watery and being retained poorly during contact in sexual intercourse.
Therefore, there continues to be a need for new personal lubricants that impart some of the benefits of both water-based lubricants (clear, easy to clean, non-staining) and silicone oil-based lubricants (highly lubricious, low osmolality). More specifically, there is a need for novel lubricants that match closely to the vaginal fluid to provide a natural alternative to commercially available personal lubricants. Furthermore, the lubricants should be compatible with lubricated and non-lubricated latex, polyurethane and synthetic PI condoms.